The blues scale is not a scale - it is merely a formalisation of many elements in blues music. One of the significant features of the playing of Robert Johnson, for example, is his heavy use of the flatted FOURTH, and if that ain't blues I'm Chinese!

Nobody's mentioned Debussy's L'apres-midi d'une faune, and that is a real exercise in the pentatonic (but not folk). For really obvious folk pentatonic stuff you need to look to pipe-and-drum tunes, such as the old Breton tune Pat-a-Pat-a-Pan, which were designed to be played on what was effectively a tin whistle with only the first three holes open ( so that the player could strike the drum with the other hand).